1. Technical Field
The invention generally pertains to ink jet printers, and particularly, to such printers using a binary imaging solution and multiple drop size ink jet print head technology.
2. Description of the Prior Art
A binary imaging solution uses colorants that each comprise a mixture of two ink components, where the two components are combined at the time the colorant is applied to a recording surface. Traditionally, to use a binary imaging solution in an ink jet printer, one channel of colorant per channel of reactant is used to ensure proper mixture of the two-part solution. This implementation, although feasible, has never really seen wide range adoption due to the cost associated with ink jet print head assemblies. In effect, this implementation would require double the number of print heads as compared to a uniary imaging solution.
As the demand for higher print quality and speeds has progressed in digital ink jet printing, print head technology has progressed in kind, starting from airbrush technology, having print resolutions of 4-9 dpi, to the newer drop-on-demand ink jets, having print resolutions up to 2400 dpi. At the older resolutions of sub-10 dpi it did not take many print heads to deliver acceptable printing speed considering that the size of the printed dot was 1/10 of an inch. Now consider that to generate images in the range of 1200 dpi the drop size would need to be 1/1200 of an inch. When working with drop sizes so small it takes many more drops to get an acceptable fill pattern when working with solid colors. This can only be accomplished in one of two ways: populate more ink jets into the product to increase coverage per pass of the print head array; or interlace many more print head passes of the print head array with the same number of print heads.
The first option would drive up printer cost to an unacceptable level, while the second option would drop productivity to unacceptable levels.
With the advancement in print head technology into grey scale functionality, the print head technology for grey scale functionality has provided an answer to this issue. These print heads generate multiple drop sizes from the same nozzle assembly. Therefore, one can generate a larger drop size when a good solid fill pattern is needed and a smaller drop size when higher detail is needed.
Prior to the introduction of grey scale print head technology the application of a binary imaging fluid was somewhat hampered also. For example, a traditional ink jet printer may have four color channels, including Cyan, Magenta, Yellow and blacK (CMYK). Other color channels employing colors such as White, Blue, Red, Orange and Green may also be used to increase functionality and color gamut. For these examples it is assumed that a printer uses seven color channels, one each for Cyan, Magenta, Yellow, blacK White, Blue, and Red, (CMYKWBR).
In traditional methods, for the application of binary solutions one of two options is selected. The first option is to use only one channel of reactant (CMYKWBRr), whereby one drop of reactant is applied to a location in an ‘OR’ methodology, where it would be applied to any drop location that is slated to receive, or already has received, a colorant drop. This method, although acceptable for a surface preparation type of implementation or an over coating application, is not effective for accurate metering of the binary mixture ratio. This is because each printed location could have anywhere from one to seven colorant drops placed in that location and only one drop of reactant. The ratio of reactant to colorant drops, assuming similar drop sizes, could be anywhere from 1:7 to 1:1. This is the method taught by Allen (U.S. Pat. No. 5,635,969), whereby the reactant channel is used as a pre coat for the colorant to control dot gain and other print artifacts.
A second option would be to have one channel of reactant per channel of colorant to provide for accurate mixing of the solution (CrMrYrKrWrBrRr). To provide the same speed and functionality as the previous example it would require 14 separate channels to provide accurate ratio metering at speed. This method is taught by Vollert (U.S. Pat. No. 4,599,627), whereby every drop of colorant is matched to a single drop of reactant to ensure a consistent ratio.
Although this solution is functional in providing an accurate mixture of the binary solutions in a controlled ratio, it is largely cost prohibitive due to the volume of additional print heads needed and ancillary equipment needed to support them as compared to uniary print systems.
Thus, a heretofore unaddressed need exists in the industry to address the aforementioned deficiencies and inadequacies in connection with binary imaging.